1. Field of the Invention
The present invention relates generally to a combination resilient and non-resilient downstop seal for use within a surface controlled subsurface safety valve.
2. Description of the Related Art
Subsurface safety valves are commonly used in wells to prevent uncontrolled fluid flow through the well in the event of an emergency, such as to prevent a well blowout. Conventional safety valves use a flapper, which is biased by a spring to a normally closed position, but is retained in an open position by the application of hydraulic fluid operating on a rod piston connected to the flapper valve from the earth's surface. A typical surface controlled subsurface safety valve ("SCSSV") is shown and described in U.S. Pat. No. 4,161,219, which is commonly assigned hereto.
Previous subsurface safety valves typically incorporate either a non-resilient seal such as a metal-to-metal seal or some type of resilient, or yieldable, seal such as an elastomeric or a non-elastomeric, plastic, seal to seal the rod piston actuator within the hydraulic actuation chamber when the subsurface safety valve is in an open position. Elastomeric seals have proven to be undesirable in certain applications wherein dissolved gases may be introduced into the elastomeric seals, which can cause an explosive decompression of the elastomeric seal from a sudden release of pressure upon opening of the safety valve, thus destroying the elastomeric seal during operation. Non-resilient metal-to-metal seals have proven to be generally reliable, although they may not provide a suitable seal in certain applications, and may permit some fluid to pass through the seal, particularly when debris is introduced into the seal creating a leak path, thus causing some leakage to occur. Non-elastomeric seals will generally provide a sufficient seal, but they may be less reliable than metal-to-metal seals in particular applications.
The necessary selection between the use of metal-to-metal seals and resilient, or yieldable, seals have not previously provided an adequate sealing solution for existing SCSSV downstops. Accordingly, there has developed a need to provide a combination non-resilient and resilient, sealing assembly to provide the benefits of both a non-resilient seal and a resilient seal in a single sealing assembly. The present invention has been contemplated to meet this need.